The present invention relates to stirring of molten metal during its continuous casting by means of an electromagnetic inductor producing a rotating field and surrounding the upper end portion of an ingot mold for the continuous casting of metal.
Inductors of the type considered are usually static polyphase inductors of annular form surrounding the ingot mold. These inductors usually comprise an annular, closed magnetic yoke provided with a plurality of poles projecting radially inwardly from the yoke, uniformly displaced from each other in the circumferential direction of the latter and each provided with an exciter winding.
Inductors of this type, as well as their application for the continuous casting of metal, are for instance described in the French Pat. No. 2,315,344 (IRSID) or No. 2,279,500 (Usinor). These inductors when mounted around the product to be cast will produce a magnetic field rotating about the axis of the metal cast and thus cause rotation of the liquid metal.
As is well known, especially during casting of steel, a controlled stirring of the liquid metal improves the quality of the casting produced, particularly as far as the structure of solidification is concerned.
It is likewise known that, in addition, it is possible to avoid inclusion in the cast metal by placing the inductor in the region of the upper end of the ingot mold to thereby centrifuge the free upper level of the cast metal in the latter.
Thus the inductor is usually placed at the upper level of the ingot mold to assure its maintenance at a proper temperature by cooling with a primary cooling water which cools the mold.
Such a process, to the industrial development of which the company to which the present application is assigned has made considerable contributions, is known to the public under the name "Magnetogyr Process".
This technique is generally practiced at all installations for the continuous casting of long product (billets, blooms, etc.).
However, a certain problem arises if the ingot mold is equipped with a system for detecting the level of the meniscus, formed at the upper free face of the rotating liquid metal, by means of gamma rays. As is known, such a system comprises an emitter of gamma rays and a receiver, for instance an ionization chamber, between which the cast metal passes, in which the metal in its upper portion is transversed by the bundle of rays, the diameter of which at the axis of the casting has to be sufficiently large in order to intercept the region of the flutuations of the height of the meniscus.
In the case of an ingot mold equipped with such a detecting system, it is usually not possible to place an inductor as high around the ingot mold as desired since the plurality of poles provided with the exciter windings present at the heads of the exciter windings, which project beyond the magnetic yoke, as well as the latter itself constitute a shield for the gamma rays.